The UK could develop a more flexible approach to environmental protection free of "spirit-crushing" Brussels directives if it votes to leave the EU, the farming minister, George Eustice, has said.

The leave camp says that, in the event of a Brexit vote, £2bn would be earmarked for conservation spending out of the money it expects to recoup from payments to Brussels

Speaking to the Guardian, the pro-Brexit minister said a leave vote in the 23 June referendum would free up a £2bn green dividend that could be spent on insurance schemes and incentives for farmers.

Environmental laws that have helped protect endangered species and clean up dirty beaches are seen one of the key achievements of the EU, but Eustice sought to reassure green-minded voters that the UK could develop better protections by going it alone.

“The birds and habitats directives would go,” he said, referring to two key pieces of European environmental law. “A lot of the national directives they instructed us to put in place would stay. But the directives’ framework is so rigid that it is spirit-crushing.

“If we had more flexibility, we could focus our scientists’ energies on coming up with new, interesting ways to protect the environment, rather than just producing voluminous documents from Brussels.”

The leave camp says that, in the event of a Brexit vote, £2bn would be earmarked for conservation spending out of the money it expects to recoup from payments to Brussels.

“Our objective would be to put in place a government-backed insurance scheme, similar to the one in Canada, to protect farmers from bad weather, crop failures and drops in prices,” Eustice said. “We would also have a whole suite of accreditation schemes run by the Soil Association, Rivers Trust and RSPCA to incentivise farmers to do positive things for the environment.”

But Eustice’s fellow environment minister Rory Stewart told the Guardian that EU membership was crucial to the UK’s environmental protections.

“It is European action that put a stop to the devastating impact on our forests of acid rain, and we are now tackling air quality by cutting harmful emissions. Through the EU we have improved more than 9,000 miles of rivers since 2010 and our water environment is in the healthiest state for 25 years,” he said.

“We have preserved valuable marine life through ending the wasteful practice of throwing fish back, dead, into the sea with a Europe-wide ban on discarding many species of fish. From tackling harmful chemicals that damage the ozone layer to cracking down on the black-market ivory trade, the UK has a strong track record in driving up environmental standards across Europe.”

Environmentalists said they feared a developmental free-for-all on sites shielded by the EU’s Natura 2000 scheme, including Snowdonia, the Lake District, the Thames estuary, the North Yorkshire Moors, Scotland’s Flow Country and Dartmoor.

One of the original authors of EU environmental legislation was Stanley Johnson, Boris’s father, who now co-chairs Environmentalists for Europe. He said of Eustice’s proposal: “I am absolutely shocked and horrified at what looks like a no-holds-barred attack by the Brexiteers on an agreed consensus that the environment benefits from a common approach.

“Don’t tell me that a new Brexit-led British government is going to put environmental regulations at top of its pile on June 24. It is not going to happen.”

The European commission is reviewing the birds and habitats directives – which define Europe’s conservation strategy – and is under unprecedented public pressure not to water them down.

The origin of the “fitness check” lies in a domestic review instigated by George Osborne in 2011, when he told parliament that the “gold-plating” of EU habitat rules was imposing “ridiculous costs” on business.

Martin Harper, the conservation director of the RSPB, said: “These nature directives have been the cornerstone of nature conservation in Europe since coming into force. Not only have they improved the fortunes of threatened species but they are essential if we want to meet our international biodiversity commitments.”

On pesticides, Eustice said the EU’s precautionary principle needed to be reformed in favour of a US-style risk-based approach, allowing faster authorisation.

“A precautionary approach is the right thing to do but it should be based on realistic assessments of risk and not just theoretical hazards,” he said. “That is the wrong way to go about it.”

The marine strategy directive would also be scrapped, Eustice said. He cited a dispute with Brussels over the UK’s failure to designate protected marine areas for harbour porpoises as an example of over-regulation, when dolphin-repelling electronic devices could have been used on nets instead.

However, the Whale and Dolphin Conservation Society said electronic pingers could already be used under current EU nature laws, which also protect porpoises from trawling, dredging, pile driving and noise from military sonars.

Clive Lewis, the shadow energy and climate change spokesperson, said: “It is absurd to suggest that Brexit could be good for the environment when the major challenges we face, not least the risk of catastrophic climate change, are international by their nature.”